Chilly Meters?

So what's up with these gas meters that are all wrapped up in green? Are they suffering from winter chills that will cause them to underestimate the amount of gas burned during the cold months?

Or perhaps the green is a larval shell and once it is moulted, we get the boulder-like meter covering (below.)

How do I know it's not just a big rock? Because of the little door down at ground level, of course.